There are a considerable number of indicators available which actively measure the pressure drop across a filter. When the pressure drop gets high enough a suitable indicating reference signal is provided and the operator knows it is time to replace the filter. These indicators are not too reliable because they do not provide any compensation for variations in the viscosity of the liquid or the flow through the filter. It can be appreciated that such indicators are not very satisfactory for vehicular implement, transmission or engine systems because the viscosity of the oils and liquids used therein significantly increases at cold temperatures and the flow through the filter varies across a relatively wide range.
Recommended filter change periods are usually published or posted, but there is still no inexpensive way to know between these theoretical intervals if the filter element is plugged, if the filter is ruptured, or if the contamination rate is excessively high. Usually, an operator does not notice a problem until serious damage has already occurred in the liquid system.
Several electro-optical systems are known for directing a light beam through the liquid and providing from scattered light a signal proportional to the particle concentration. But these systems are expensive, are not as reliable as desired since air bubbles can affect results, and do not give a reading on the condition of the filter.
Other systems operate on a magnetic principle so that the degree of contamination by non-metallic particles is not measured.
U.S. Pat. No. 3,499,315 issued Mar. 10, 1970 to J. A. Marino discloses another method of determining contamination in a fluid system by recording the pressure differential produced across a filter element. However, it involves temporary connections and undesirable controlling of the flow so that it is not an integrated system with diagnostic capability, but rather is more of a specialized test set up.
Accordingly, what is needed is an improved contamination monitor for detecting and quantifying the amount of liquid-borne contamination in a vehicle liquid system or the like, and for operationally communicating with the system service filter and indicating the condition thereof while compensating for viscosity and flow. Preferably, the improved contamination monitor should be capable of being programmed to take information from the liquid system at preselected periods of time and should be capable of providing recognizable output information so as to indicate to the operator the specific nature of any abnormal condition such as an excessively fast rate of filter plugging.
The present invention is directed to overcoming one or more of the problems as set forth above.